June 4, 2010

If you have not read the home page on Why Basements Leak please read that page before proceeding onto this page.

Interior Waterproofing
Interior waterproofing consists of the use of either painting the wall with ‘waterproof’ paint; applying vapor barrier plastics to the walls, or the use of sump pumps. Click for exterior waterproofing.

Paint Products
Products such as Drylock, Watertite, Damplock claim to prevent water form passing thru it. The claim is true, yet water coming thru a foundation wall will simply peal the paint from the concrete it was painted to. These products only really prevent dampness over a very short period and keep the wall from showing the visible effect water leaves: mold, staining, mortar erosion. These products are very popular with people selling property as they give the appearance of a very clean wall. But if you come back in 6 months most of the mold stains and loose mortar will again be very apparent.

So what benefit do these types of paints have? They are best suited for concrete walls that are not below ground in any way. They are also well suited for exterior use where there is not moisture coming through the substrate (the surface painted upon).

Vapor BarriersVapor barriers are sheets of solid plastic or vinyl that are applied to foundation wall to prevent moisture from entering the interior living space. These are sometimes installed outside or on the inside walls attached directly to the concrete. If these sheets are not applied before framing and drywall it is not really possible to apply them without removing the drywall and framing first thus requiring replacement and extra cost. Vapor barriers that simply rest on the floor will serve little purpose as they will just allow any moisture to collect on the floor damaging carpet, drywall etc. Vapor barriers need to run into and under the floor to allow the water entry to the drainage system. Anything less than this will not give the water anywhere else to go and will cause a mold and or flooding problem.

See how the white vapor barrier is installed in the photo below.

Interior Waterproofing SystemsIn the picture above you can see the section of floor that is removed to install the black 4″ drainage pipe that runs along the footer and pours into the well. The pipe itself should have a 1:18 downward pitch to ease movement of water to the pump. After it is installed then the gravel, black MiraDrain (sitting in an L-shape next to and below the floor) is installed and vapor barrier is attached to the wall to prevent wall condensation to the insulation or drywall. If drywall is present it will very often need the bottom 6″ or more removed to allow the floor to be removed and for installation of the system to be possible. Most commonly the drainage pipe will have a mud sock placed over it to prevent silt and mud from entering the system thereby clogging it. If there is no clay or dirt then a mud sock does not need to be used.

This technique of sheeting the wall with vapor barrier and running it beneath the floor to a subfloor system is considered among any company that warranties against dampness to be the surest way to guarantee water from entering a finished below ground area. This is not to say that outside system do not have any merit, but that it is almost impossible for these types of interior systems to fail. Unless..

The sump pump fails.
Interior waterproofing systems must rely on a sump pump to push the collected water outside and away from the foundation if the electricity goes out or the pump stops operating for whatever reason the water can flood out of the sump well (this is relatively contained and much better than the whole foundation leaking, but still can be a mess.) This problem can be prevented with the use of battery back-up sump pumps (even though they are known to be quite often very finicky). The best solution is to not give a sump well more than 200 ft. of system to collect and drain. The idea here is that the wells themselves can hold a lot of water and can endure the lack of operation of one of the pumps due to failure or electrical outage.